For the last few years, cable modem systems based on data-over-cable service interface specifications (DOCSIS) have been accepted as a “last mile” high-speed data solution for the consumers.
A two-way Hybrid Fiber-Coax (HFC) cable network is an infrastructure capable of supporting multiple overlaying networks, viz. analog or digital video service, high-speed data, and telephony service. Each of these services uses different band of the available spectrum in the downstream and upstream directions, and each service has its own operations and provisioning infrastructure. At customer premises, a full-service subscription requiring multiple boxes of customer premises equipment (CPE) such as a set top box, a telephone network interface unit, and a cable modem. These overlaying services are inefficient in terms of increasing the cost of operations and the cost of consumer ownership.
Convergent Network
It is therefore highly desirable to have a converged network, capable of delivering voice, video and data in a unified communications infrastructure.
Although later versions of data-over-cable media-access-control (MAC) have quality-of-service (QoS) capability by using polling, the protocol essentially is based on sharing an upstream and a downstream channel. Switching users among channels is complex and slow.
Moreover, the cable modem has severe limitations when it comes to supporting digital video services. Conventional digital video (broadcast or video on demand) requires more stringent bit-error-rate than data services. High bit rate of approximately 20 Mbps per HDTV movie channel is required, significantly impacting the capacity of the other services residing in the same downstream channel.
Upstream Limitations
The upstream bandwidth of a HFC network is limited by the amount of available spectrum in the upstream in a “sub-split” HFC cable plant which is between 5 to 42 MHz in North America. Because of ingress interference, a good portion of the spectrum is not suitable for wide-band (e.g. 3.2 MHz or 6.4 MHz per channel) and higher-order modulations (e.g. 16, 32, or 64 QAM) to achieve a high capacity for the upstream channel in use. If a 6.4 MHz channel is used, only 6.4/(42−5)=17% of the upstream spectrum is used. The other 83% of the spectrum (in particular for frequencies below 10 MHz) is often unused. Conventional data-over-cable MAC is quite limited in handling multiple channels, in increasing the capacity, and providing the quality of service (QoS) required by different services.
Moreover, since each upstream channel must support the packets generated by different services with different QoS requirements, it is very difficult to achieve high channel utilization under dynamically changing traffic conditions. In particular, the overhead of the MAC management packets such as bandwidth request and initial calibration can be significant and will complicate the scheduling efficiency of the cable modem termination system (CMTS).
The conventional data-over-cable MAC protocol relies on some form of polling to achieve QoS goal of meeting bandwidth, latency and jitter requirements. For a polling interval of 2 ms, each upstream channel requires about 270 Kbps of downstream bandwidth for the MAC operation. This represents a significant amount of bandwidth taken from the downstream channel. Therefore, scalability of using multiple upstream channels in conventional data-over-cable is quite limited.
Broadcast Quality Digital Video
Although the HFC network has sufficient bandwidth to support delivery of a full spectrum of services including data, telephony and video, these services currently are separate infrastructures, each being provisioned by a service provider. Consequently sub-optimal usage of the HFC spectrum and costly duplication of equipment at the head end and at customer premises are resulted. Voice-over-IP enables convergence of voice and data. However, video service remains using a separate infrastructure.
Therefore, there is an unmet need for a unified communication system that can provide the full need of broadband Internet access, IP telephony, broadcast quality digital video over the same HFC system.
Therefore, there is an unmet need for a MAC that can be used to implement a full-service cable modem system to fulfill the full potential of a HFC network for delivery voice, video and data cost-effectively to the home and the business.
It will be realized after the detailed description of the invention how to overcome the limitations of conventional cable modem systems by the novel MAC and system architecture. A highly efficient and scalable access method can be used to deliver simultaneously interactive digital video, telephony and high speed internet access as well as interactive gaming shared by a large number of users. The MAC fully utilizes the upstream and downstream spectrum enabling service providers economically deploy the services without a forklift upgrade to the HFC cable plant currently deployed for conventional cable modem service. The unified full-service communication system will reduce the cost of providing three separate provisioning systems for video, data and voice, simplify head end equipment and at the same time reduce the number of on-premises equipment from three to one.
It is an object of the present invention to overcome the disadvantages of the prior art.